1. Field of the Invention
The present invention relates to a light intensity detection device which includes a photoelectric device (photoelectric semiconductor device) having electric output characteristics which change in accordance with incident light intensity to detect the intensity of incident light which varies incident angle in accordance with incident angle caused by the movement of a light source such as the sun.
2. Discussion of the Related Art
A light intensity detection device has been used to detect visible incident light, infrared light, or other light using a photoelectric device for environment measurement or for control of various instruments based on the detected signals. For example, for all air conditioner in an automobile to control temperature in the cabin, only measurement of temperatures inside and outside the cabin using a temperature sensor and the control of temperature inside the cabin based on these measurements are not adequate to achieve a comfortable temperature in the cabin of the car. This is because if the sunlight entering the car hits people seated in these cabin, the people become warmer than the cabin temperature even if the temperature inside the cabin is low. Accordingly, in an air conditioner for an automobile, in addition to the temperature sensors inside and outside the car, a light intensity detection device is used to detect the amount of light entering the cabin of the car for control of temperatures in the cabin based on the detected results.
A conventional light intensity detection device is described in Japan Patent kokai No. 61(1986)-210915, which comprises a photoelectric device having a tight receiving surface, and a filter, which is arranged before the light receiving surface, and which includes a transparent resin plate which is coated with a light-proof agent or to which a light-proof agent is adhered. In this construction, by determining the concentration of the light screen according to the incident angles of light, amount of light entering the area covered with the filter is reduced to adjust the sensitivities of the photoelectric device to the incident angles, which allows detection of light with a similar sensitivity which enters the light receiving surface not only at the right angle but at an inclined angle.
However, in this conventional light amount detection device, the filter, which is arranged in front of the light receiving surface, including the transparent, resin plate which is coated with a light-proof agent or to which a light-proof agent is adhered, has to be assembled, which results in an increased number of parts and machining processes and causes a complicate construction.
Moreover, if light horizontally enters the light receiving surface of the photoelectric device, a sufficient output level cannot be obtained, which is detrimental to a stable output characteristic to all the incident light through the entire area from the vertical to the horizontal directions and makes it hard to gain a desired output characteristics to the incident angles even if necessary because of the complicated construction.